System, method and apparatus that employ virtual private networks to resist IP QoS denial of service attacks

ABSTRACT

A network architecture in accordance with the present invention includes a communication network that supports one or more network-based Virtual Private Networks (VPNs). The communication network includes a plurality of boundary routers that are connected by access links to CPE edge routers belonging to the one or more VPNs. To prevent traffic from outside a customer&#39;s VPN (e.g., traffic from other VPNs or the Internet at large) from degrading the QoS provided to traffic from within the customer&#39;s VPN, the present invention gives precedence to intra-VPN traffic over extra-VPN traffic on each customer&#39;s access link through access link prioritization or access link capacity allocation, such that extra-VPN traffic cannot interfere with inter-VPN traffic. Granting precedence to intra-VPN traffic over extra-VPN traffic in this manner entails special configuration of network elements and protocols, including partitioning between intra-VPN and extra-VPN traffic on the physical access link using layer 2 multiplexing and the configuration of routing protocols to achieve logical traffic separation between intra-VPN traffic and extra-VPN traffic at the VPN boundary routers and CPE edge routers. By configuring the access networks, the VPN boundary routers and CPE edge routers, and the routing protocols of the edge and boundary routers in this manner, the high-level service of DoS attack prevention is achieved.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to communication networks and, inparticular, to the prevention of denial of service attacks in a publiccommunication network, for example, the Internet. Still moreparticularly, the present invention relates to method, system andapparatus for preventing denial of service attacks in a communicationnetwork having a shared network infrastructure by separating theallocation and/or prioritization of access capacity to traffic of siteswithin a virtual private network (VPN) from the allocation and/orprioritization of access capacity to sites in another VPN or the publicnetwork.

[0003] 2. Description of the Related Art

[0004] For network service providers, a key consideration in networkdesign and management is the appropriate allocation of access capacityand network resources between traffic originating from VPN customersites and traffic originating from outside the VPN (e.g., from theInternet or other VPNs). This consideration is particularly significantwith respect to the traffic of VPN customers whose subscription includesa Service Level Agreement (SLA) requiring the network service providerto provide a minimum communication bandwidth or to guarantee aparticular Quality of Service (QoS). Such service offerings require thenetwork service provider to implement a network architecture andprotocol that achieve a specified QoS and ensure sufficient accesscapacity and network resources are available for communication withother VPN sites separate from communication with hosts that are not partof the VPN.

[0005] In Internet Protocol (IP) networks, a straightforward approach toachieving QoS and implementing admission control comparable to that ofconnection-oriented network services, such as voice or AsynchronousTransfer Mode (ATM), is to emulate the same hop-by-hop switchingparadigm of signaling resource reservations for the flow of IP packetsrequiring QoS. In fact, the IP signaling standard developed by theInternet Engineering Task Force (IETF) for Integrated Services (Intserv)adopts precisely this approach. As described in IETF RFC 1633, Intservis a per-flow IP QoS architecture that enables applications to chooseamong multiple, controlled levels of delivery service for their datapackets. To support this capability, Intserv permits an application at atransmitter of a packet flow to use the well-known Resource ReSerVationProtocol (RSVP) defined by IETF RFC 2205 to request a desired QoS classat a specific level of capacity from all network elements along the pathto a receiver of the packet flow. After receiving an RSVP PATH messagerequesting a resource reservation and an RSVP RESV message confirmingresource reservation from an upstream node, individual network elementsalong the path implement mechanisms to control the QoS and capacitydelivered to packets within the flow.

[0006]FIG. 1 illustrates the implications of utilizing a conventionalIntserv implementation to perform admission control. As shown in FIG. 1,an exemplary IP network 10 includes N identical nodes (e.g., serviceprovider boundary routers) 12, each having L links of capacity X coupledto Customer Premises Equipment (CPE) 14 for L distinct customers. In aper-flow, connection-oriented approach, each node 12 ensures that nolink along a network path from source to destination is overloaded.Looking at access capacity, a per-flow approach is able tostraightforwardly limit the input flows on each of the ingress accesslinks such that the sum of the capacity for all flows does not exceedthe capacity X of any egress access link (e.g., Link 1 of node 12 a). Asimilar approach is applicable to links connecting unillustrated corerouters within IP network 10.

[0007] Although conceptually very simple, the admission controltechnique illustrated in FIG. 1 has a number of drawbacks. Mostimportantly, Intserv admission control utilizing RSVP has limitedscalability because of the processing-intensive signaling RSVP requiresin the service provider's boundary and core routers. In particular, RSVPrequires end-to-end signaling to request appropriate resource allocationat each network element between the transmitter and receiver, policyqueries by ingress node 12 b-12 d to determine which flows to admit andpolice their traffic accordingly, as well as numerous other handshakemessages. Consequently, the processing required by Intserv RSVPsignaling is comparable to that of telephone or ATM signaling andrequires a high performance (i.e., expensive) processor component withineach boundary or core IP router to handle the extensive processingrequired by such signaling. RSVP signaling is soft state, which meansthe signaling process is frequently refreshed (by default once every 30seconds) since the forwarding path across the IP network may change andtherefore information about the QoS and capacity requested by a flowmust be communicated periodically. This so-called soft-state mode ofoperation creates an additional processing load on a router even greaterthan that of an ATM switch. Furthermore, if the processor of a boundaryrouter is overloaded by a large number of invalid RSVP requests, theprocessor may crash, thereby disrupting service for all flows for allcustomers being handled by the router with the failing processor.

[0008] In recognition of the problems associated with implementingadmission control utilizing conventional Intserv RSVP signaling, theIETF promulgated the Differentiated Services (Diffserv or DS) protocoldefined in RFC 2475. Diffserv is an IP QoS architecture that achievesscalability by conveying an aggregate traffic classification within a DSfield (e.g., the IPv4 Type of Service (TOS) byte or IPv6 traffic classbyte) of each IP-layer packet header. The first six bits of the DS fieldencode a Diffserv Code Point (DSCP) that requests a specific class ofservice or Per Hop Behavior (PHB) for the packet at each node along itspath within a Diffserv domain.

[0009] In a Diffserv domain, network resources are allocated toaggregates of packet flows in accordance with service provisioningpolicies, which govern DSCP marking and traffic conditioning upon entryto the Diffserv domain and traffic forwarding within the Diffservdomain. The marking (i.e., classification) and conditioning operationsneed be implemented only at Diffserv network boundaries. Thus, ratherthan requiring end-to-end signaling between the transmitter and receiverto establish a flow having a specified QoS, Diffserv enables an ingressboundary router to provide the QoS to aggregated flows simply byexamining and/or marking each IP packet's header.

[0010] Although the Diffserv standard addresses Intserv scalabilitylimitation by replacing Intserv's processing-intensive signaling with asimple per packet marking operation that can easily be performed inhardware, implementation of the Diffserv protocol presents a differenttype of problem. In particular, because Diffserv allows host marking ofthe service class, a Diffserv network customer link can experience aDenial of Service (DoS) attack if a number of hosts send packets to thatlink with the DS field set to a high priority. It should be noted that aset of hosts can exceed the subscribed capacity of a Diffserv serviceclass directly by setting the DSCP or indirectly by submitting trafficthat is classified by some other router or device to a particular DSCP.In Diffserv, an IP network can only protect its resources by policing atthe ingress routers to ensure that each customer interface does notexceed the subscribed capacity for each Diffserv service class. However,this does not prevent a DoS attack.

[0011]FIG. 2 depicts a DOS attack scenario in an exemplary IP network10′ that implements the conventional Diffserv protocol. In FIG. 2, anumber of ingress nodes (e.g., ingress boundary routers) 12 b′-12 d′each admit traffic targeting a single link of an egress node (e.g.,egress boundary router) 12 a′. Although each ingress nodes 12′ policesincoming packets to ensure that customers do not exceed their subscribedresources at each DSCP, the aggregate of the admitted flows exceeds thecapacity X of egress Link 1 of node 12 a′, resulting in a denial ofservice to the customer site served by this link.

SUMMARY OF THE INVENTION

[0012] In view of the limitations attendant to conventionalimplementations of the Intserv and Diffserv standards, the presentinvention recognizes that it would be useful and desirable to provide amethod, system and apparatus for data communication that support acommunication protocol that, unlike conventional Intservimplementations, is highly scalable and yet protects against the DoSattacks to which conventional Diffserv and other networks aresusceptible.

[0013] A network architecture in accordance with the present inventionincludes a communication network that supports one or more network-basedVirtual Private Networks (VPNs). The communication network includes aplurality of boundary routers that are connected by access links to CPEedge routers belonging to the one or more VPNs. To prevent traffic fromoutside a customer's VPN (e.g., traffic from other VPNs or the Internetat large) from degrading the QoS provided to traffic from within thecustomer's VPN, the present invention gives precedence to intra-VPNtraffic over extra-VPN traffic on each customer's access link throughaccess link prioritization or access link capacity allocation, such thatextra-VPN traffic cannot interfere with inter-VPN traffic. Grantingprecedence to intra-VPN traffic over extra-VPN traffic in this mannerentails special configuration of network elements and protocols,including partitioning between intra-VPN and extra-VPN traffic on thephysical access link and access network using layer 2 switching andmultiplexing, as well as the configuration of routing protocols toachieve logical traffic separation between intra-VPN traffic andextra-VPN traffic at the VPN boundary routers and CPE edge routers. Byconfiguring the access networks, the VPN boundary routers and CPE edgerouters, and the routing protocols of the edge and boundary routers inthis manner, the high-level service of DoS attack prevention isachieved.

[0014] Additional objects, features, and advantages of the presentinvention will become apparent from the following detailed writtendescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The novel features believed characteristic of the invention areset forth in the appended claims. The invention itself however, as wellas a preferred mode of use, further objects and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawings, wherein:

[0016]FIG. 1 depicts a conventional Integrated Services (Intserv)network that implements per-flow QoS utilizing RSVP;

[0017]FIG. 2 illustrates a conventional Differentiated Services(Diffserv) network that implements QoS on aggregated traffic flowsutilizing DSCP markings in each packet header and is thereforevulnerable to a Denial of Service (DoS) attack;

[0018]FIG. 3 depicts an exemplary communication network that, inaccordance with a preferred embodiment of the present invention, resistsDoS attacks by partitioning allocation and/or prioritization of accesscapacity by reference to membership in Virtual Private Networks (VPNs);

[0019]FIG. 4 illustrates an exemplary network architecture that providesa CPE-based VPN solution to the DoS attack problem;

[0020]FIG. 5 is a more detailed block diagram of a QoS-aware CPE edgerouter that may be utilized within the network architectures depicted inFIGS. 4 and 7;

[0021]FIG. 6A is a more detailed block diagram of a QoS-aware boundaryrouter without VPN function that may be utilized within the networkarchitectures illustrated in FIGS. 4 and 7;

[0022]FIG. 6B is a more detailed block diagram of a QoS-aware boundaryrouter having VPN function that may be utilized within the networkarchitecture illustrated in FIG. 4;

[0023]FIG. 7 illustrates an exemplary network architecture that providesa network-based VPN solution to the DoS attack problem; and

[0024]FIG. 8 is a more detailed block diagram of a QoS-aware VPNboundary router that may be utilized within the network architecturedepicted in FIG. 7.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0025] With reference again to the figures and, in particular, withreference to FIG. 3, there is depicted a high level block diagram of anexemplary network architecture 20 that, in accordance with the presentinvention, provides a scalable method of providing QoS to selectedtraffic while protecting a Virtual Private Network (VPN) customer'saccess and trunk network links against DoS attacks. Similar to the priorart network illustrated in FIG. 2, network architecture 20 of FIG. 3includes a Diffserv network 21 having N service provider boundaryrouters (BRs) 22 that each have L access links. What is different innetwork architecture 20 is that Diffserv network 21 supports a pluralityof VPN instances, of which two are shown in the figure as identified bythe access links of boundary routers 22 coupled to CPE edge routers(ERs) for a first network service customer 24 and an ER for a secondnetwork service customer 25 at each of four sites, respectivelyidentified by letters a through d. Each CPE ER provides network serviceto a customer's local area networks (LANs). The service providernetwork-based VPN may support many more customers than the two shown inthis figure.

[0026] In the exemplary communication scenario depicted in FIG. 3, hostswithin the LANs of the first VPN customer coupled to CPE edge routers 24b-24 d, those within a second VPN customer's LANs coupled to CPE edgerouters 25 a-25 d, as well as sites coupled to other unillustrated CPEedge routers linked to boundary routers 22 a-22 d, may all transmitpacket flows targeting the LAN coupled to the first VPN customer CPEedge router 24 a. If the conventional Diffserv network of the prior artdescribed above with respect to FIG. 2 were implemented, the outgoingaccess link 1 of boundary router 22 a coupled to CPE edge router 24 acould be easily overwhelmed by the convergence of these flows, resultingin a DoS. However, in accordance with the present invention, Diffservnetwork 21 of FIG. 3 prevents a DoS attack from sites outside the VPN bydirecting intra-VPN traffic to a first logical port 27 on physicalaccess link 1 of boundary router 22 a, while directing traffic fromother VPNs or other sites to a second logical port 28 on physical accesslink 1 of boundary router 22 a.

[0027] To prevent traffic from outside a customer's community ofinterest (e.g., traffic from other VPNs or the Internet at large) fromdegrading the QoS provided to traffic from within the customer'scommunity of interest (e.g., traffic from other hosts in the samebusiness enterprise), the present invention either prioritizes intra-VPNtraffic over extra-VPN traffic, or allocates access link capacity suchthat extra-VPN traffic cannot interfere with inter-VPN traffic. In otherwords, as described in detail below, each boundary router 22 givesprecedence on each customer's access link to traffic originating withinthe customer's VPN, where a VPN is defined herein as a collection ofnodes coupled by a shared network infrastructure in which networkresources and/or communications are partitioned based upon membership ofa collection of nodes. Granting precedence to intra-VPN traffic overextra-VPN traffic in this manner entails special configuration ofnetwork elements and protocols, including partitioning of the physicalaccess between intra-VPN and extra-VPN traffic using layer 2multiplexing and the configuration of routing protocols to achievelogical traffic separation. In summary, the configuration of the CPEedge router, the access network, the network-based VPN boundary routerand the routing protocols involved in the edge and boundary routerscooperate to achieve the high-level service of DoS attack prevention, asdetailed below. Conventional Diffserv and CPE edger router IPsec-basedIP VPN implementations, by contrast, do not segregate traffic destinedfor sites within the same VPN (i.e., intra-VPN traffic) and traffic sentfrom other regions of the Internet (i.e., extra-VPN traffic).

[0028] Referring now to FIGS. 4-8, at least two classes ofimplementations of the generalized network architecture 20 depicted inFIG. 3 are possible. In particular, a network in accordance with thepresent invention can be realized as a CPE-based VPN implementation, asdescribed below with reference to FIGS. 4-6, or as a network-based VPNimplementation, as described below with reference to FIGS. 7-8.

[0029] Referring first to FIG. 4, there is illustrated an exemplarynetwork architecture 30 that employs a CPE-based VPN to resist DoSattacks. The depicted network architecture includes a Diffserv-enabledIP VPN network 44, a best effort IP public network 46, and a pluralityof customer Local Area Networks (LANs) 32. Customer LANs 32 each includeone or more hosts 48 that can function as a transmitter and/or receiverof packets communicated over one or both of networks 44 and 46. In theexemplary implementation illustrated in FIG. 4, it is assumed thatcustomer LANs 32 a and 32 b belong to the same community of interest(i.e., VPN), such as a business enterprise.

[0030] Each customer LAN 32 is coupled by a respective CPE edge router34 and physical access link 35 to a respective access network (e.g., anL2 access network) 38. Access networks 38 a and 38 b each have a firstL2 access logical connection to a boundary router (BR) 40 ofDiffserv-enabled IP VPN network 44 and a second L2 access logicalconnection to a boundary router (BR) 42 of best effort IP public network46. As illustrated in FIG. 4 by differing line styles representingintra-VPN and extra-VPN traffic, VPN-aware CPE edge routers 34 a and 34b route only packets with IP address prefixes belonging to the IP VPNvia Diffserv-enabled IP VPN network 44, and route all other traffic viabest effort IP public network 46. To enhance security of customer LANs32, CPE edge routers 34 a and 34 b send all traffic to and from besteffort IP public network 46 through a respective one of firewalls 36 aand 36 b.

[0031] In the network architecture illustrated in FIG. 4, DoS attacksoriginating outside of the IP VPN are prevented by configuration ofboundary routers 40 a-40 b and 42 a-42 b to appropriately utilize thetwo logical connections of access networks 38 a and 38 b to grantprecedence to intra-VPN traffic. For example, in a first configuration,a higher priority is assigned to the L2 access logical connection withDiffserv-enabled IP VPN network 44 than to the L2 access logicalconnection with best effort public IP network 46. L2 access networksthat support such prioritization of access links 35 include Ethernet(e.g., utilizing Ethernet priority), ATM (e.g., utilizing ATM servicecategories), and many frame relay (FR) network implementations. Theseimplementations can each be provisioned utilizing well-known techniques.With this configuration, each boundary router 40 of Diffserv enabled IPVPN network 44 shapes the transmission rate of packets to its logicalconnection to access network 38 to a value less than that of the accesslink to prevent starvation of the L2 access logical connection to besteffort IP public network 46. Alternatively, in a second configuration,boundary routers 40 a-40 b and 42 a-42 b may be individually configuredto shape the traffic destined for each L2 access network logicalconnection to a specified rate, where the sum of these rates is lessthan or equal to the transmission capacity of the physical access mediumlinking CPE edge routers 34 and access networks 38. In either of thesealternative configurations, boundary routers 40 and 42 performscheduling and prioritization based upon packets' DSCP markings andshape to the capacity allocated to the access network connection for IPVPN traffic.

[0032] As will be appreciated by those skilled in the art, selection ofwhich of the alternative configurations to implement is a matter ofdesign choice, as each configuration has both advantages anddisadvantages. For example, with the first configuration, coordinationof the access network configuration between networks 44 and 46 iseasier. However, if access networks 38 implement only strict priority,then IP VPN traffic from Diffserv-enabled IP VPN network 44 may starvebest effort traffic communicated over IP public network 46. The secondconfiguration addresses this disadvantage by allocating a portion of theaccess link capacity to each type of network access (i.e., bothintra-VPN and extra-VPN). However, if boundary routers 40 and 42 shapetraffic in accordance with the second configuration, unused accesscapacity to one of networks 44 and 46 cannot be used to access the othernetwork. That is, since the shapers are on separate boundary routers 40and 42, only non-work-conserving scheduling is possible.

[0033] With reference now to FIG. 5, there is illustrated a moredetailed block diagram of a QoS-aware CPE edge router 34 that may beutilized within the network architecture depicted in FIG. 4. Asillustrated, CPE edge router 34 includes a number of LAN ports 60, whichprovide connections for a corresponding number of customer LANs 32. Forexample, in FIG. 5, LAN port 60 a is connected to a customer LAN 32including a number of hosts 48 respectively assigned 32-bit IP addresses“a.b.c.d,” “a.b.c.e.,” and “a.b.c.f.”

[0034] Each LAN port is also coupled to a forwarding function 62, whichforwards packets between LAN ports 60 and one or more logical ports(LPs) 66 residing on one or more Wide Area Network (WAN) physical ports64 (only one of which is illustrated). LPs 66, which each comprise alayer-2 sub-interface, may be implemented, for example, as an EthernetVirtual LAN (VLAN), FR Data Link Connection Identifier (DLCI), ATMVirtual Channel Connection (VCC), or Point-to-Point Protocol(PPP)/High-Level Data Link Control (HDLC) running on a Time DivisionMultiplexed (TDM) channel. WAN physical port 64 employs a scheduler 68to multiplex packets from logical ports 64 onto the transmission mediumof an access network 38 and forwards packets received from accessnetwork 38 to the respective logical port utilizing a forwardingfunction 70.

[0035] When a LAN port 60 of CPE edge router 34 receives packets from acustomer LAN 32, the packets first pass through a classifier 80, whichdetermines by reference to a classifier table 82 how each packet will behandled by CPE edge router 34. As illustrated in FIG. 5, classifiertable 82 may have a number of indices, including Source Address (SA) andDestination Address (DA), Source Port (SP) and Destination Port (DP),Protocol Type (PT), DSCP, or other fields from packets' link, network ortransport layer headers. Based upon a packet's values for one or more ofthese indices, classifier 72 obtains values for a policer (P), marker(M), destination LP, and destination LP queue (Q) within CPE edge router34 that will be utilized to process the packet. In alternativeembodiments of the present invention, lookup of the destination LP anddestination LP queue entries could be performed by forwarding function62 rather than classifier 80.

[0036] As shown, table entry values within classifier table 82 may befully specified, partially specified utilizing a prefix or range, ornull (indicated by “-”). For example, the SAs of hosts 48 of LAN 32 arefully specified utilizing 32-bit IP addresses, DAs of severaldestination hosts are specified utilizing 24-bit IP address prefixesthat identify particular IP networks, and a number of index values andone policing value are null. In general, the same policer, marker,and/or shaper values, which for Intserv flows are taken from RSVP RESVmessages, may be specified for different classified packet flows. Forexample, classifier table 82 specifies that policer P1 and marker M1will process packets from any SA marked with DSCP “101” as well aspackets having a SA “a.b.c.e” marked with DSCP “010.” However,classifier table 82 distinguishes between flows having differentclassifications by specifying different destination LP values fortraffic having a DA within the VPN (i.e., intra-VPN traffic) and trafficaddressed to hosts elsewhere in the Internet (i.e., extra-VPN traffic).Thus, because IP address prefixes “r.s.t,” “w.x.y,” and “l.m.n” allbelong to the same VPN as network 32, traffic matching these DAs is sentvia LP-1 66 a to other sites within the same VPN over theDiffserv-enabled IP VPN network 44 while all other traffic is sent viaLP-2 66 b to best effort IP public network 46.

[0037] The logical port 66 and LP queue to which packets are forwardedcan be determined by static configuration or dynamically by a routingprotocol. In either case, a VPN route should always have precedence overan Internet route if a CPE router 34 has both routes installed for thesame destination IP address. Such priority can be achieved in any ofseveral ways, including (1) use of Interior Gateway Protocol (IGP)(i.e., OSPF and IS-IS) to install VPN routes and EBGP or static routingto install Internet routes or (2) use of EBGP to install both VPN routesand Internet routes, with a higher local preference being given for VPNroutes.

[0038] After classification, packets are policed and marked, asappropriate, by policers P0, P1 and markers M0, M1, M2 as indicated byclassifier table 82 and then switched by forwarding function 62 toeither logical port 66 a or 66 b, as specified by the table lookup.Within the specified logical port 66, packets are directed to the LPqueues Q0-Q02 specified by classifier table 82. LP queues Q0-Q2 performadmission control based upon either available buffer capacity orthresholds, such as Random Early Detection (RED). A scheduler 90 thenservices LP queues Q0-Q2 according to a selected scheduling algorithm,such as First In, First Out (FIFO), Priority, Weighted Round Robin(WRR), Weighted Fair Queuing (WFQ) or Class-Based Queuing (CBQ). Forexample, in the illustrated embodiment, scheduler 90 of LP-2 66 aimplements WFQ based upon the weight w_(i) associated with each LP queuei and the overall WFQ scheduler rate r₂ for logical port 2, therebyshaping traffic to the rate r₂. Finally, as noted above, scheduler 68 ofphysical WAN port 64 services the various logical ports 66 to controlthe transmission rate to access network 38.

[0039] CPE edge router 34 receives packets from access network 38 at WANphysical port 64 and then, utilizing forwarding function 70, forwardspackets to the appropriate logical port 66 a or 66 b as indicated byconfiguration of access network 38 as it maps to the logical ports. Ateach logical port 66, packets pass through a classifier 100, whichgenerally employs one or more indices within the same set of indicesdiscussed above to access a classifier table 102. In a typicalimplementation, the lookup results of classifiers 100 are less complexthan those of classifier 80 because policing and marking areinfrequently required. Thus, in the depicted embodiment, packets areforwarded by forwarding function 62 directly from classifiers 100 oflogical ports 66 to the particular queues Q0-Q2 of LAN port 60 aspecified in the table lookup based upon the packets' DSCPs. Asdescribed above, queues Q0-Q2 of LAN port 60 a are serviced by ascheduler 102 that implements WFQ and transmits packets to customer LAN32.

[0040] Referring now to FIG. 6A, there is depicted a more detailed blockdiagram of a QoS-aware boundary router without any VPN function, whichmay be utilized within the network architecture of FIG. 4, for example,to implement boundary routers 42. As shown, boundary router 42 of FIG.6A includes a plurality of physical ports 116, a plurality of logicalports 110 coupled to access network 38 by a forwarding function 112 forincoming packets and a scheduler 114 for outgoing packets, and aforwarding function 118 that forwards packets between logical ports 110and physical ports 116. The implementation of multiple physical ports116 permits fault tolerant connection to network core routers, and theimplementation of multiple logical ports coupled to access network 38permits configuration of one logical port (i.e., LP-1 110 a) as aDiffserv-enabled logical port and a second logical port (i.e., LP-2 110b) as a best-effort logical port.

[0041] Thus, for traffic communicated from access network 38 throughLP-2 110 b of boundary router 42 towards the network core, classifier124 of LP-2 110 b directs all packets to marker M0 in accordance withclassifier table 126. Marker M0 remarks all packets received at LP-2 110b with DSCP 000, thus identifying the packets as best-effort traffic.Classifier 120 of LP-1 110 a, by contrast, utilizes classifier table 122to map incoming packets, which have already received DSCP marking at atrusted CPE (e.g., service provider-managed CPE edge router 34), intoqueues Q0-Q2 on PHY-1 116 a, which queues are each associated with adifferent level of QoS. Because the packets have already beenmulti-field classified, marked and shaped by the trusted CPE, boundaryrouter 42 need not remark the packets. If, however, the sending CPE edgerouter were not a trusted CPE, boundary router 42 would also need toremark and police packets received at LP-1 110 a.

[0042] Following classification (and marking in the case of trafficreceived at LP-2 110 b), traffic is forwarded to an appropriate physicalport 116 or logical port 110 by forwarding function 118. In contrast toedge router 34 of FIG. 5, which utilizes classifiers to perform the fullforwarding lookup, boundary router 42 employs an alternative design inwhich forwarding function 118 accesses forwarding table 128 with apacket's DA to determine the output port, namely, LP-1 110 a, LP-2 110b, or PHY-1 116 a in this example. In the case of a non-VPN router,forwarding table 128 is populated by generic IP routing protocols (e.g.,Border Gateway Protocol (BGP)) or static configuration (e.g.,association of the 24-bit IP address prefix “d.e.f.” with LP-2 110 b).An alternative implementation could centrally place the IP lookupforwarding function in forwarding function 62. The exemplaryimplementation shown in FIG. 6 assumes that boundary router 42 sends alltraffic bound for the network core to only one of the physical ports 116connected to a core router. In other embodiments, it is possible, ofcourse, to load balance traffic across physical ports 116. In addition,implementations omitting the core router or employing one or morelogical ports to one or more core routers are straightforward extensionsof the depicted design.

[0043] For traffic communicated to access network 38 through boundaryrouter 42, classifier 132 accesses classifier table 134 utilizing theDSCP of the packets to direct each packet to the appropriate one ofqueues Q0-Q-2 for the QoS indicated by the packet's DSCP. For a customerthat has purchased a Diffserv-enabled logical port 110, this has theeffect of delivering the desired QoS since the source CPE has policedand marked the flow with appropriate DSCP value. Although a best-effortcustomer is capable of receiving higher quality traffic, preventing sucha one-way differentiated service would require significant additionalcomplexity in the classifier and include distribution of QoS informationvia routing protocols to every edge router in a service providernetwork.

[0044] With reference now to FIG. 6B, there is depicted a more detailedblock diagram of a QoS-aware VPN boundary router 40, which may beutilized to provide Diffserv-enabled and DoS-protected VPN servicewithin the network architecture depicted in FIG. 4. As shown, boundaryrouter 40 includes a plurality of physical ports 226 for connection tocore routers of Diffserv-enabled IP VPN network 44, a plurality ofDiffserv-enabled logical ports 224 coupled to an access network 38 by aforwarding function 220 for incoming packets and a scheduler 222 foroutgoing packets, and a forwarding function 228 that forwards packetsbetween logical ports 224 and physical ports 226.

[0045] Each Diffserv-enabled logical port 224 implemented on boundaryrouter 40 serves a respective one of a plurality of VPNs. For example,Diffserv-enabled logical port LP-A 224 a serves a customer sitebelonging to VPN A, which includes customer sites having the 24-bit IPaddress prefixes “a.b.c.” and “a.b.d.” Similarly, Diffserv-enabledlogical port LP-B 224 b serves a customer site belonging to VPN B, whichincludes two customer sites having the 24-bit IP address prefixes“b.c.d.” and “b.c.e.” Diffserv-enabled logical ports 224 do not servesites belonging to best effort IP public network 46 since such trafficis routed to boundary routers 42, as shown in FIG. 4.

[0046] As further illustrated in FIG. 6B, each core-facing physical port226 of boundary router 40 is logically partitioned into a plurality ofsub-interfaces implemented as logical tunnels 240. As will beappreciated by those skilled in the art, a tunnel may be implementedutilizing any of a variety of techniques, including an IP-over-IPtunnel, a Generic Routing Encapsulation (GRE) tunnel, an IPsec operatedin tunnel mode, a set of stacked Multi-Protocol Label Switching (MPLS)labels, a Layer 2 Tunneling Protocol (L2TP), or a null tunnel. Suchtunnels can be distinguished from logical ports in that routinginformation for multiple VPNs can be associated with a tunnel in anested manner. For example, in the Border Gateway Protocol (BGP)/MPLSVPNs described in IETF RFC 2547, the topmost MPLS label determines thedestination boundary router while the bottommost label determines thedestination VPN.

[0047] In operation, a classifier 230 on each of Diffserv-enabledlogical ports 224 classifies packets flowing from access network 38through boundary router 40 to the network core of Diffserv-enabled IPVPN network 44 in accordance with the packets' DSCP values by referenceto a respective classifier table 232. As depicted, classifier tables 232a and 232 b are accessed utilizing the DSCP as an index to determine theappropriate one of queues Q0-Q2 on physical port PHY-1 226 a for eachpacket. Packets received by physical ports 226 are similarly classifiedby a classifier 250 by reference to a classifier table 254 to determinean appropriate one of queues Q0-Q2 for each packet on one of logicalports 224. After classification (and optional (re)marking as shown atLP-B 224 b), forwarding function 228 switches packets between logicalports 224 and physical ports 226 by reference to VPN forwarding tables234 a-234 n, which are each associated with a respective VPN. Thus, forexample, VPN forwarding table 234 a provides forwarding routes for VPNA, and VPN forwarding table 234 b provides forwarding routes for VPN B.

[0048] VPN forwarding tables 234 are accessed utilizing the source portand DA as indices. For example, in the exemplary network configurationrepresented in forwarding table 234 a, traffic within VPN A addressedwith a DA having a 24-bit IP address prefix of “a.b.d.” traverses TNL-1240 a, and traffic received at TNL-1 240 b is directed to LP-A 224 a.Similar routing between TNL-2 240 b and LP-B 224 b can be seen in VPNrouting table 234 b. As discussed above, VPN forwarding tables 234 canbe populated by static configuration or dynamically utilizing a routingprotocol.

[0049] Following processing by forwarding function 178, packets are eachdirected to the output port queue corresponding to their DSCP values.For example, packets marked with the QoS class associated with DSCP 101are placed in Q2, packets marked with the QoS class associated with DSCP010 are placed in Q1, and traffic marked with DSCP 000 is placed in Q0.Schedulers 236 and 252 then schedule output of packets from queues Q0-Q2to achieve the requested QoS.

[0050] With reference now to FIG. 7, there is illustrated an exemplarynetwork architecture 150 that provides a network-based VPN solution tothe DoS attack problem. In FIG. 7, like reference numerals and trafficnotations are utilized to identify features corresponding to features ofnetwork architecture 30 depicted in FIG. 4.

[0051] As depicted, network architecture 150 of FIG. 7, like networkarchitecture 30 of FIG. 4, includes a Diffserv-enabled IP VPN network44, a best effort IP public network 46, and a plurality of customerLocal Area Networks (LANs) 32. As above, customer LANs 32 a and 32 bbelong to the same VPN and each include one or more hosts 48 that canfunction as a transmitter and/or receiver of packets. Each customer LAN32 is coupled by a CPE edge router 34 and a physical access link 153 toa respective access network (e.g., an L2 or L3 access network) 154. Incontrast to access networks 38 of FIG. 4, which have separate logicalconnections for QoS and best effort traffic, access networks 154 areonly connected to boundary routers 156 of Diffserv-enabled IP VPNnetwork 44, which have separate logical connections to boundary routers42 of best effort IP public network 46. Thus, intra-VPN traffic destinedfor network 44 and extra-VPN traffic destined for network 46 are bothrouted through boundary routers 156, meaning that work-conservingscheduling between the two classes of traffic is advantageouslypermitted. However, as a consequence, the complexity of boundary routers156 necessarily increases because each boundary router 156 mustimplement a separate forwarding table for each attached customer, aswell as a full Internet forwarding table that can be shared amongcustomers.

[0052] Referring now to FIG. 8, there is depicted more detailed blockdiagram of a QoS-aware VPN boundary router in which the policers,shapers, schedulers, logical port access network connections andforwarding tables are configured to provide Diffserv-enabled andDoS-protected VPN service within the network architecture depicted inFIG. 7. As shown, boundary router 156 includes a plurality of physicalports 176 for connection to network core routers, a plurality ofDiffserv-enabled logical ports 174 coupled to access network 154 by aforwarding function 170 for incoming packets and a scheduler 172 foroutgoing packets, and a forwarding function 178 that forwards packetsbetween logical ports 174 and physical ports 176.

[0053] Because each CPE edge router 34 is coupled to a boundary router156 by only a single access link through access network 154, eachnetwork customer site is served at boundary router 156 by a pair ofDiffserv-enabled logical ports 174, one for intra-VPN traffic and onefor extra-VPN traffic. For example, Diffserv-enabled logical ports LP-A1174 a and LP-A2 174 serve a single customer site belonging to VPN A,which includes at least two customer sites having the 24-bit IP addressprefixes “a.b.c.” and “a.b.d.” In the depicted embodiment, LP-A1 174 aprovides access to QoS traffic communicated across Diffserv-enabled IPVPN network 44 to and from sites belonging to VPN A, while LP-A2 174 bprovides access to best effort traffic to and from best effort IP publicnetwork 46.

[0054] As further illustrated in FIG. 8, each core-facing physical port176 of boundary router 156 is logically partitioned into a plurality ofsub-interfaces implemented as logical tunnels 180. As will beappreciated by those skilled in the art, a tunnel may be implementedutilizing any of a variety of techniques, including an IP-over-IPtunnel, a Generic Routing Encapsulation (GRE) tunnel, an IPsec operatedin tunnel mode, a set of stacked Multi-Protocol Label Switching (MPLS)labels, or a null tunnel. Such tunnels can be distinguished from logicalports in that routing information for multiple VPNs can be associatedwith a tunnel in a nested manner. For example, in the Border GatewayProtocol (BGP)/MPLS VPNs described in IETF RFC 2547, the topmost MPLSlabel determines the destination boundary router while the bottommostlabel determines the destination VPN.

[0055] In operation, a classifier 182 on each of Diffserv-enabledlogical ports 174 classifies packets flowing from access network 154through boundary router 156 to the network core in accordance with thepackets' DSCP values by reference to a respective classifier table 190.As depicted, classifier tables 190 a and 190 b are accessed utilizingthe DSCP as an index to determine the appropriate one of queues Q0-Q2 onphysical port PHY-1 176 a for each packet. Packets received by physicalports 176 are similarly classified by a classifier 198 by reference to aclassifier table 192 to determine an appropriate one of queues Q0-Q2 foreach packet on one of logical ports 174. After classification (andoptional (re)marking as shown at LP-A2 174 b), forwarding function 178switches packets between logical ports 174 and physical ports 176 byreference to VPN forwarding tables 194 a-194 n, which are eachassociated with a respective VPN and shared Internet forwarding table195. Thus, for example, forwarding table 194 a contains entriesproviding forwarding routes for VPN A, while Internet forwarding table195 contains entries providing forwarding routes for packets specifyingLP-A2 or TNL-2 (i.e., the logical interfaces configured for Internetaccess) as a source.

[0056] Forwarding tables 194 are accessed utilizing the source port andDA as indices. For example, in the exemplary network configurationrepresented in forwarding table 194 a, intra-VPN traffic addressed witha DA having a 24-bit IP address prefix of “a.b.d.” traverses TNL-1 180a, while extra-VPN (i.e., Internet) traffic traverses TNL-2 180 b (whichcould be a null tunnel). Forwarding table 194 a further indicates thatintra-VPN traffic received via TNL-1 180 a is directed to LP-A1 174 a,and all other traffic arriving from the Internet via tunnel TNL-2 180 baddressed with a DA having a 24-bit IP address prefix of “a.b.c.” issent to LP-A2 174 b. Traffic that terminates to other ports on boundaryrouter 156 (i.e., traffic having a Local DA) is sent to other ports ofboundary router 156 (indicated as LP-x). In other words, the entries inforwarding table 194 a marked “Local” specify address prefixes otherthan those assigned to VPNs (e.g., a.b.c/24) that are assigned tointerfaces on boundary router 156.

[0057] Following processing by forwarding function 178, packets are eachdirected to the output port queue corresponding to their DSCP values.For example, packets marked with the QoS class associated with DSCP 101are placed in Q2, packets marked with the QoS class associated with DSCP010 are placed in Q1, and best effort traffic marked with DSCP 000 isplaced in Q0. Schedulers 196 then schedule output of packets from queuesQ0-Q2 to achieve the requested QoS.

[0058] As has been described, the present invention provides an improvednetwork architecture for providing QoS to intra-VPN traffic whileprotecting such flows against DoS attack from sources outside the VPN.The present invention provides DoS-protected QoS to selected flowsutilizing a network-based VPN service and a best effort Internet serviceconnected to a CPE edge router using a L2 access network withappropriately configured routing protocols. Diffserv marking at the edgeand handling in the network-based VPN core provides QoS to selectedflows while logically partitioning intra-VPN and extra-VPN traffic toprevent DoS to a VPN network customer site due to traffic originatingfrom outside of the customer's VPN exceeding that site's accesscapacity. Even further protection from traffic originating from withinthe customer's VPN is possible using Intserv policy control, implementedon the CPE edge router and/or the QoS-aware boundary router, asdescribed in IETF RFC 2998, incorporated herein by reference.

[0059] The network architecture of the present invention may be realizedin CPE-based and network-based implementations. The CPE-basedimplementation permits easy configuration of the access networks linkingthe CPE edge routers and service provider boundary routers and permitsQoS to be offered to VPN sites without implementing Diffserv across theentire service provider network. The network-based configurationadvantageously permits work conserving scheduling that permits extra-VPNtraffic to utilize excess access capacity allocated to intra-VPNtraffic.

[0060] While various embodiments of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Thus, the breadth and scopeof the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents. For example,although the present invention has been described with respect topreferred embodiments in which network-based VPNs are implemented withina Diffserv network, it should be understood that the present inventionis not restricted to use with Diffserv networks, but is instead to othernetwork-based VPNs, which may be implemented, for example, utilizingBGP/MPLS as taught in RFC 2547 or virtual routers as taught in RFC 2917.In addition, although FIGS. 3, 4 and 7 illustrate the connection of eachCPE edge router to a VPN network and a best effort network by one accesslink, it should be understood that, for redundancy, a CPE edge routermay be connected by multiple access links to one or more accessnetworks, which provide logical connections to one or more boundaryrouters of each of the VPN and best effort networks. In such “dualhoming” implementations, the multiple access links can be utilized ineither a primary/backup or load-sharing arrangement through installationof static routes in the service provider boundary routers or dynamicconfiguration of the service provider boundary routers utilizing routingprotocols (e.g., EBGP). This would require that the CPE edge routerimplement multiple forwarding tables and separate instances of therouting protocol for the VPN and Internet access address spaces. Theimplementation of such a CPE edge router would be similar to thatillustrated in FIG. 8 and described in the associated text, with only asingle VPN table and a single table for Internet routes.

What is claimed is:
 1. A network system that resists denial of serviceattacks on an access link to a destination host belonging to a virtualprivate network (VPN), said network system comprising: one or moreegress boundary routers having connections to an access networkincluding the access link, wherein said one or more egress boundaryrouters transmit intra-VPN traffic from sources within the VPN andextra-VPN traffic from sources outside the VPN within separate accessnetwork logical connections for intra-VPN and extra-VPN traffic; and aplurality of ingress boundary routers coupled to the one or more egressboundary routers for communication utilizing a network-based VPNprotocol that logically partitions intra-VPN and extra-VPN traffic, suchthat denial of service attacks on said access link originating fromsources outside the VPN can be prevented.
 2. The network system of claim1, and further comprising a Differentiated Services network coupling atleast one of the plurality of ingress boundary routers and at least oneof the one or more egress boundary routers.
 3. The network system ofclaim 1, and further comprising a plurality of customer premisesequipment (CPE) edge routers each coupled to a respective one of saidplurality of ingress boundary routers.
 4. The network system of claim 1,and further comprising the access network.
 5. The network system ofclaim 4, and further comprising a customer premises equipment (CPE) edgerouter to the access link.
 6. The network system of claim 5, said CPEedge router having a physical port coupled to said access link, saidphysical port implementing a first logical port for intra-VPN trafficand a second logical port for extra-VPN traffic.
 7. The network systemof claim 1, wherein at least one of said plurality of ingress boundaryrouters implements a plurality of tunnels that logically partitionintra-VPN and extra-VPN traffic.
 8. The network system of claim 1,wherein said one or more egress boundary routers provide a plurality ofdifferent qualities of services to said intra-VPN traffic.
 9. A networksystem, comprising: an access network having an access link to adestination host belonging to a virtual private network (VPN), whereinsaid access network supports a first logical connection for intra-VPNtraffic from sources within the VPN and a second logical connection forextra-VPN traffic from sources outside the VPN; one or more egressboundary routers having connections to the access network, wherein saidone or more egress boundary routers transmit intra-VPN traffic towardthe destination host via the first logical connection and transmitextra-VPN traffic toward the destination host via the second logicalconnection; and a plurality of ingress boundary routers coupled to theone or more egress boundary routers for communication utilizing anetwork-based VPN protocol that logically partitions intra-VPN andextra-VPN traffic, such that denial of service attacks on said accesslink originating from sources outside the VPN can be prevented.
 10. Thenetwork system of claim 9, and further comprising a DifferentiatedServices network coupling at least one of the plurality of ingressboundary routers and at least one of the one or more egress boundaryrouters.
 11. The network system of claim 9, and further comprising aplurality of customer premises equipment (CPE) edge routers each coupledto a respective one of said plurality of ingress boundary routers. 12.The network system of claim 9, and further comprising a customerpremises equipment (CPE) edge router to the access link.
 13. The networksystem of claim 12, said CPE edge router having a physical port coupledto said access link, said physical port implementing a first logicalport for intra-VPN traffic and a second logical port for extra-VPNtraffic.
 14. The network system of claim 9, wherein at least one of saidplurality of ingress boundary routers implements a plurality of tunnelsthat logically partition intra-VPN and extra-VPN traffic.
 15. Thenetwork system of claim 9, wherein said one or more egress boundaryrouters provide a plurality of different qualities of services to saidintra-VPN traffic.
 16. A method of protecting an access link to adestination host belonging to a virtual private network (VPN) againstdenial of service attacks, said method comprising: in an access networkincluding the access link, providing a first logical connection forintra-VPN traffic from sources within the VPN and a second logicalconnection for extra-VPN traffic from sources outside the VPN;communicating, from a plurality of ingress boundary routers to one ormore egress boundary routers, intra-VPN and extra-VPN traffic destinedfor said destination host, wherein said intra-VPN traffic and saidextra-VPN traffic are transmitted utilizing a network-based VPN protocolthat logically partitions intra-VPN and extra-VPN traffic; transmittingintra-VPN traffic from said one or more egress boundary routers towardthe destination host via the first logical connection, and transmittingextra-VPN traffic from said one or more egress boundary routers towardthe destination host via the second logical connection, such that denialof service attacks on said access link originating from sources outsidethe VPN can be prevented.
 17. The method of claim 16, wherein saidcommunicating comprises communicating utilizing a DifferentiatedServices protocol.
 18. The method of claim 16, wherein a customerpremises equipment (CPE) edge router is coupled between said accessnetwork and said destination host, said method further comprising: at aphysical port of the CPE edge router coupled to the access link,providing first and second logical ports; and receiving intra-VPNtraffic at the first logical port, and receiving extra-VPN traffic atthe second logical port.
 19. The method of claim 16, and furthercomprising logically partitioning intra-VPN and extra-VPN traffic by atleast one of said plurality of ingress boundary routers utilizing aplurality of tunnels.
 20. The method of claim 16, and further comprisingsaid one or more egress boundary routers providing a plurality ofdifferent qualities of services to said intra-VPN traffic.